Design and performance of collimated coincidence point sources for simultaneous transmission measurements in 3-D PET

We have implemented a simultaneous emission-transmission measurement for three-dimensional positron emission tomography (3-D PET) using a collimated coincidence point source design employing a fast, dedicated, reference detector close to the transmission source. This design reduces the effects of randoms, scatter, dead time, and sensitivity loss on the emission data compared to previous implementations. It also greatly reduces the effect of emission contamination of the transmission data compared to the use of rod sources. In this paper, we present performance characterizations of this measurement technique on both the Siemens/CTI ECAT ART and PET/SPECT tomographs. The main effect of the transmission sources on the emission measurement is an increased randoms rate, which leads to a 10-25% reduction in NECR at specific activities >2 kBq/mL in a 21-cm-diameter phantom on the PET/SPECT. Emission contamination effects on the transmission measurement are estimated to be less than I % for up to 20 kBq/mL in a 21-cm phantom on the PET/SPECT. Both the emission and transmission NECR are dominated by the effects of randoms. Considering the effects of both emission and transmission noise on the final corrected image, it appears that 3-6 kBq/mL of emitter concentration is an optimal imaging range for simultaneous acquisitions. We present the first images of a normal volunteer using this system on a Siemens/CTI PET/SPECT tomograph.